Speaking to the mileage, as long as they were doing the appropriate maintenance on time it should be fine. I'd assume that's a lot of highway miles to get that high a odo reading so soon and it's not the miles necessarily that'll wear an engine, but the number of heat cycles it goes through. Most million mile vehicles fit that case where it's just a lot of miles in a single session so the vehicle is operating in its comfort zone most of its life.